The present invention relates to a voltage supply circuit, a power supply circuit, a display driver, an electro-optic device and an electronic apparatus.
An active-matrix liquid crystal display includes a plurality of scanning lines and a plurality of data lines arranged in a matrix. The display also includes a plurality of switching elements each of which is coupled to a scanning line and a data line, and a plurality of pixel electrodes each of which is coupled to a switching element. Each pixel electrode is placed face to face with an opposing electrode with a liquid crystal (electro-optic material in a broad sense) therebetween.
With the liquid crystal display of this configuration, voltage supplied to a data line via a switching element that has been turned on by a selected scanning line is applied to a pixel electrode. Depending on this voltage applied between the pixel electrode and a corresponding opposing electrode, the transmission of the pixel varies.
Liquid crystals in liquid crystal displays have to be driven in an alternate manner so as to prevent deterioration of the liquid crystals. Therefore, liquid crystal displays provide polarity inversion driving that inverts the polarity of the voltage between a pixel electrode and an opposing electrode every frame or plural horizontal scanning periods. The polarity inversion driving can be provided by changing the voltage supplied to the opposing electrode in sync with polarity inversion timing, for example.
To provide this polarity inversion driving, voltage boosted by charge-pump operation is directly supplied to the opposing electrode, for example. Alternatively, voltage boosted by charge-pump operation is used as a power supply voltage of a voltage regulation circuit in order to supply an output from the voltage regulation circuit to the opposing electrode, for example. JP-A-2001-100177 and JP-A-2002-366114 are examples of related art.
The charge-pump operation involves little power loss with high efficiency, but requires a capacitance element to stabilize boosted voltage. Furthermore, supplying a voltage boosted by this charge-pump operation directly to the opposing electrode degrades picture quality because of a voltage decline caused by a leak between the opposing and pixel electrodes. To avoid this degradation, a large-capacity capacitance element and a low-leak liquid crystal panel are required, which will in turn increase costs.
Meanwhile, supplying an output from the voltage regulation circuit to the opposing electrode as mentioned above can stabilize the voltage of the opposing electrode with high accuracy, while that requires to make the power supply voltage of the voltage regulation circuit about one volt higher than the output voltage of the voltage regulation circuit. It is thus necessary to drive the opposing electrode from lower-potential voltage to higher-potential voltage, or higher-potential voltage to lower-potential voltage whenever voltage applied to the opposing electrode is switched by the polarity inversion driving. As a result, a large amount of power is consumed.